In addition to contamination from landfills, septic tanks, spills, and human error, some natural occurrences influence water quality. For example, some groundwater sources are brackish, so water drawn from these sources will be saline rather than fresh. Alternatively, some aquifers and formations include higher levels of total dissolved solids than others. Likewise, naturally occurring microorganisms appear in higher numbers depending on the source.
Climate change and natural disasters can affect water quality independent of human involvement or industrial operations. Droughts can reduce the overall recharge rate of aquifers, producing not only lower levels of water but higher levels of total dissolved solids. Natural disasters such as floods can also introduce contaminants to water sources. Even though the contaminants may be manmade, their introduction to the water source is a natural occurrence.
USGS Study of Well Contamination
In 2015, almost 43 million Americans supplied their own home water and over 98 percent of that water came from groundwater. In 2009, the U.S. Geological Survey (USGS) studied the water quality of over 2,000 private wells to measure the existence and extent of contamination. The study found that about 23 percent of them did have at least one contaminant at a level of potential health concern. And the contaminants that were most frequently at those levels were mostly from natural geologic sources, coming from the rocks and sediment that make up the aquifers from which the wells were drawing water—things like radon, arsenic, uranium, manganese and nitrate.2
1. Data map from USGS: https://www.usgs.gov/media/images/people-using-domestic-supply-wells-square-kilometer
2. USGS, 2018, “Contamination in U.S. Private Wells”, https://www.usgs.gov/special-topics/water-science-school/science/contamination-us-private-wells (accessed 12/19/2022)
Images: “Epecuen (Dead City), Argentina” by De Visu via Shutterstock; “Domestic-wells-USGS” by USGS